1. Field of the Invention
The present invention relates to a rotation detection circuit of a dc brushless motor using a fixed bias voltage, and more particularly to a rotation detection circuit that may be selectively applied in either a fixed bias voltage manner or connected with a zener diode to thereby ensure that a transistor is completely cut off by a low level input from the driver circuit, and that the transistor is absolutely controlled at a saturation state or a cutoff state by the high or low level.
2. Description of the Related Art
FIG. 1 is a circuit diagram of a driver circuit and a rotation detection circuit (phantom lines) of a dc brushless motor in accordance with the prior art. FIG. 2 is a schematic view of an output waveform outputted by a driver of the drive circuit of a dc brushless motor in accordance with the prior art. As shown in FIG. 1, the conventional motor drive circuit 1 includes a driver ICI, and two coils L1 and L2. A hall bolt module and a control module (transistor) are built in the driver IC 1. A hall member is used to detect changing of a magnetic field of a permanent magnet of a rotor, and a weak hall voltage is amplified, and then two terminals OUT 1 and OUT2 of the driver ICI continuously output a current alternating to the two coils L1 and L2. The two coils L1 and L2 are excited to rotate the rotor. As shown in FIG. 2, the two output terminals OUT 1 and OUT2 of the driver ICI simultaneously output two opposite phases of a square waveform. Referring back to FIG. 1, the conventional rotation detection circuit 10 of a dc brushless motor includes a transistor Q1, and a resistor R1 performed as an amplifier circuit.
Another conventional rotation detection circuit of a dc brushless motor is disclosed in Taiwanese Patent Publication No. 337386, which discloses a sensor line connected to a transistor that performs as a rotation detector. The conventional rotation detection circuit of a dc brushless motor disclosed in Taiwanese Patent Publication No. 337386 is the same as the conventional drive circuit and rotation detection circuit as shown in FIG. 1. However, the conventional rotation detection circuit is only available for a low current driven motor and unavailable for a high current driven motor. If the conventional rotation detection circuit is applied in a high current driven motor, the conventional rotation detection circuit will output an incorrect signal 11 waveform.
FIG. 3 is a schematic view of the waveform of the detection signal outputted by the conventional rotation detection circuit of a dc brushless motor as shown in FIG. 1, wherein the conventional rotation detection circuit is applied in a high current driven motor. When high current drives the motor, the voltage VCE between an emitter and a collector of a transistor of the drive 17 circuit is increased by the current passing through this emitter and this collector. According to different functions of the driver IC, the voltage VCE is about 0.2 to 0.5V while being driven by low current, and is about 0.5 to 1.5V while being driven by high current. Thus, the voltage VCE (0.5 to 1.5V) being driven by the high current is greater than a cutoff voltage 0.7V of the transistor Q1. When the motor drive circuit outputs a low level signal from the voltage VCE (0.5 to 1.5V) to the conventional rotation detection circuit, the output low level signal maybe greater than 0.7V thereby producing a vague low level. Thus, the transistor Q1 of the conventional rotation detection circuit will be conducted at a low level signal, such that the conventional rotation detection circuit will output an incorrect signal waveform due to the transistor Q1 being incompletely cutoff. As shown in FIG. 3, the conventional rotation detection circuit outputs an incorrect signal waveform as shown in phantom lines. Accordingly, the conventional rotation detection circuit outputs an incorrect signal waveform as shown in phantom line instead of a correct signal waveform as shown in solid line, such that it reduces the quality of rotation detection waveform. For solving the above-mentioned problem, it is necessary to eliminate a motor driver circuit outputting a vague low level to conduct the transistor QI of the conventional rotation detection circuit.
Accordingly, the present invention may improve the abovementioned drawbacks, wherein the rotation detection circuit may be selectively supplied with either a fixed bias voltage or connected with a zener diode to thereby ensure that a transistor is completely cut off by a low level input from the driver circuit, such that the transistor is absolutely controlled in saturation state or cutoff state by high or low level.
An objective of the present invention is to provide a rotation detection circuit of a dc brushless motor in which the rotation detection signal is adjusted based on a fixed bias voltage to thereby ensure that a transistor is completely cut off by a low level input from the driver circuit, so that the quality of the rotation detection signal is enhanced.
Another objective of the present invention is to provide a rotation detection circuit of a dc brushless motor that is connected with a zener diode to thereby ensure that a transistor is completely cut off by a low level input from the driver circuit, so that the quality of the rotation detection signal is enhanced. In accordance with the present invention, a rotation detection circuit of a dc brushless motor using a fixed bias voltage includes a transistor, and a signal adjuster. The signal adjuster is connected in series between the transistor and a driver circuit of the dc brushless motor, for adjusting a signal output of the driver circuit that is supplied from the driver circuit to the transistor in accordance with a fixed bias voltage. The signal adjuster can be selectively supplied with a fixed bias voltage or connected in series with a zener diode. The signal adjuster can be adjusted according to the characteristics of the motor driver IC, thereby enhancing the design of the rotation detection circuit.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.